This invention relates to a method for the treatment of a surface of a shaped body formed of a synthetic organic polymer for the activation of the surface.
Since synthetic organic polymers, such as polyolefins which consist only of saturated hydrocarbons and which are hydrophobic and highly crystalline in nature, generally has a low surface energy, the surfaces of shaped bodies such as sheets and fibers of such polymers are hard to be coated, printed, bonded or dyed. Therefore, it is necessary to pretreat such shaped bodies and to increase the surface energy thereof prior to coating, printing, bonding, dyeing or the like surface processing.
A variety of surface pretreating techniques have been hitherto proposed. For example, as pretreating methods for coating, printing and bonding, there are known a sand blast treatment, a treatment with solvent, a treatment with a chromic acid mixture, a flame treatment, a corona discharge treatment, a plasma treatment, a functional groups-introducing treatment and a photo-grafting treatment. These conventional methods, however, are not entirely satisfactory for the reasons as set forth below.
The sand blast treatment method is one in which granules of a grinding material are caused to impinge on a surface of a shaped body to be treated for roughing same. The granular grinding material causes fouling of the working environment and the product. The surface of the treated product is, therefore, required to be washed with water. Further, there are caused problems that the treatment makes the surface opaque and that the grinding material once cut into the surface cannot be removed.
The solvent treatment includes exposing, for a short period of time, a shaped body to vapors of a super-heated, halogenated hydrocarbon so that an amorphous portion of the surface of the shaped body is etched by swelling. It is, however, necessary to provide over the treated surface a primer layer containing chlorinated propylene prior to coating. In addition, unless the primer coat is provided immediately after the treatment, the treatment soon becomes ineffective. The treatment sometimes causes distortion of the shaped body. The treated surface should be heated for the removal of the solvent remaining after the treatment. Additionally, this method is dangerous because of the necessity to handle vapors of a halogenated hydrocarbon which also tends to cause deterioration of the apparatus.
The treatment with chromic acid mixture includes heating the mixture (containing 75 parts of potassium bichromate, 120 parts of water and 1500 parts of concentrated sulfuric acid) to about 100.degree. C., and immersing a shaped body to be treated in the heated mixture for about 5 min. This method incurs high costs for the treatment of the waste chromic acid mixture.
The flame treatment includes exposing the surface of a shaped body to be treated to an oxidizing flame (1000.degree.-2500.degree. C.) produced by the combustion of a gas containing excess air. The surface is liable to be distorted or melted by the heat.
The corona discharge treatment includes passing a film or film-like body to be treated through a space between an electrode and a metal roller while applying a high electric voltage therebetween. This method is not applicable to shaped bodies other than those of a film-like form.
The plasma treatment includes exposing the surface of a plastic body to a low temperature plasma so that the surface undergoes a chemical change by the action of dissociated oxygen and ultraviolet rays. Plasma of oxygen or air is used. This method is disadvantageous because of the necessity of an expensive apparatus.
The functional groups-introducing method includes irradiating UV rays on the surface of a shaped body in an atmosphere of chlorine, and then treating the irradiated surface with an alkali. This method poses a problem of handling very dangerous chlorine gas.
The photo-grafting method includes admixing benzophenone with polypropylene powder, forming the admixture into a film, and photo-treating the surface of the film in the presence of acrylamide in an oxygen-free atmosphere for photochemically graft-copolymerizing the acrylamide with the polypropylene. This method requires complicated steps and is economically disadvantageous.
As surface pretreatment methods for dyeing polypropylene fibers which are typical examples of fibers of an inactive polymeric material, there are proposed the following methods:
(1) a method in which the surface is oxidized with nitrogen dioxide; PA0 (2) a method in which the surface is chlorinated and, if desired, then treated with an amine; PA0 (3) a method in which the surface is sulfonated with fuming sulfuric acid and, if desired, then treated with an amine; PA0 (4) a method in which the surface is chlorosulfonated by UV irradiation in an atmosphere of sulfur dioxide gas and chlorine gas and is then treated with an amine; PA0 (5) a method in which the surface is heated after depositing thereon sulfolauric acid or sulfosalicylic acid and is then treated with an amine; PA0 (6) a method in which the surface is treated with an alkylamine, pyrrole or naphthylamine; PA0 (7) a method in which vinylpyridine or isopropenylpyridine is grafted on the surface; PA0 (8) a method in which vinyl chloroacetate or vinyl sulfonate is grafted on the surface and thereafter the surface is treated with an amine; PA0 (9) a method in which the surface is treated with an emulsion containing as a major component a chlorosulfonated polyolefin; and PA0 (10) a method in which the surface is impregnated with tetrachlorosilicon. PA0 (1) Polypropylene; PA0 (2) Copolymers of mixtures of two or more of polypropylene, polyethylene, ethylene-propylene rubber and the like polymer; PA0 (3) Ethylene-propylene rubber; PA0 (4) Copolymers or mixtures of ethylene-propylene rubber with another polymer or polymers; PA0 (5) Polyethylene; PA0 (6) Copolymers or mixtures of polyethylene with another polymer or polymers; PA0 (7) Polymethylpentene; PA0 (8) Polyacetal; PA0 (9) Copolymers or mixtures of polyacetal with another polymer or polymers; and PA0 (10) Blends of at least one of the above polymers (1)-(9) with a filler and/or an additive. PA0 (1) The treated surface gives a smooth, beautiful and strong coated, printed or dyed layer; PA0 (2) The method does not require priming: PA0 (3) The method is simple, economical and does not require a long treatment time and, therefore, it is suited for industrial applications; PA0 (4) The method may be carried out by the use of simple and inexpensive apparatus; PA0 (5) No dangerous gases such as chlorine gas are used; PA0 (6) The method does not cause deformation or melting of the surface to be treated; PA0 (7) The method is applicable to any shaped bodies such as films, fibers, rods, plates, etc; and PA0 (8) The method may be performed without generation of vapors of UV ray-absorbing organic liquid.
These methods, however, are not industrially actually applied because they cannot be performed with safety, because the treated surface still cannot be sufficiently satisfactorily dyed and because they are not economically fully acceptable.
SUMMARY OF THE INVENTION
The present invention is aimed at the provision of a method of treating an inactive or inert surface of an organic polymeric shaped body which is devoid of the defects of the conventional methods. In accordance with the present invention, there is provided a method of treating a surface of a shaped body formed of a synthetic organic polymer, comprising the steps of:
contacting said surface with a UV ray-absorbing organic liquid at a temperature and for a period of time sufficient to swell said surface; and
irradiating UV rays having wave lengths in the range of 1800-2100 .ANG. on said swollen surface thereby increasing the surface energy of said surface of the shaped body.
The present invention will be described in detail below.